Speakers
Description
It is generally known that thermal contact resistance between two bodies is a function of pressure, hardness, and thermal conductivity [1]. In most engineering cases there is a constant trade-off between the demands of the thermal design and other requirements. It is especially true for typical cubesat applications [2]. This means it may not always be feasible to apply high pressure or utilize highly thermally conductive materials characterized by sufficient hardness.
In order to address these problems at early stages of the design phase, simulation tools are used in which contact thermal resistance is a parameter defined by a thermal engineer. Since it is not always possible to perform experiments on thermal interfaces considered in the analysis, a modelling approach based on [3], [4] or [5] work is preferred. Some of them considered simplification of vacuum conditions [6] which is actually beneficial for approach used in this work. Those models usually discuss flat plates of sufficiently thick layers of material with uniform pressure distribution that is kept constant in time. These might not be always the case: pressure can be considered uniform only in direct neighborhood of a point where the force is applied (for example bolted nut connection); surfaces might not be flat (on micro scale they always have some roughness, but they also might not be planar at all, with curved contact area); force (and pressure) can change in time (deteriorating contact conductance and increasing thermal induced stresses).
Those variables were considered in this work analytically and numerically for a few types of connections, mainly bolted joints. Moreover, connections of more advanced shapes (threaded inserts) with variable pressure distribution were analyzed. Comparisons between interfaces utilizing thermal interface materials and bare metal connections were performed.
Conclusions derived from this investigation were used in a practical approach to analytically determine the equivalent thermal conductivities of bolted joints of the Intuition-1 satellite. The aim was to replace complex geometric elements in the numerical model of the satellite with one-dimensional conductors of specified overall thermal resistance. Additionally, experimental work was performed to establish contact resistance of reference copper and aluminum plates with different degrees of roughness. This allowed to choose appropriate contact conductance model. Due to small interface areas and relatively high contact pressures typical to nanosatellites, the analytical models for contact conductance were applicable. By utilizing the described method in the numerical analysis of the satellite, convergence between simulation results and measurements in the thermal-vacuum chamber was achieved.
References
[1] M.M. Yovanovich. “Four decades of research on thermal contact, gap,
and joint resistance in microelectronics”. In: IEEE Transactions on
Components and Packaging Technologies 28.2 (2005), pp. 182–206. doi:
10.1109/TCAPT.2005.848483.
[2] P. B. Hager et al. “Contact Conductance in Common CubeSat Stacks”.
In: (2019), p. 14.
[3] M. Yovanovich. “Micro and Macro Hardness Measurements, Correla-
tions, and Contact Models”. In: Collection of Technical Papers - 44th
AIAA Aerospace Sciences Meeting 16 (Jan. 2006). doi: 10.2514/6.
2006-979.
[4] M. G. Cooper, B. B. Mikic, and M. M. Yovanovich. “Thermal Contact
Conductance”. In: International Journal of Heat and Mass Transfer 12
(1969), pp. 279–300.
[5] A. Majumdar and C. L. Tien. “Fractal Characterization and Simulation
of Rough Surfaces”. In: Wear 136.2 (1990), pp. 313–327. doi: 10.1016/
0043-1648(90)90154-3.
[6] M. M. Yovanovich and H. Fenech. “Thermal Contact Conductance of
Nominally Flat Rough Surfaces in a Vacuum Environment”. In: Ther-
mophysics and Temperature Control of Spacecraft and Entry Vehicles.
Ed. by G. B. Heller. Vol. 18. New York: Academic, 1966, pp. 773–794.
